Sheet-fed offset printing machines generally have direct current speed-controlled drive motors to drive the printing cylinders of a printing machine at a desired rotational speed. Direct current motors make it possible to implement predefined rotational speed ramps for increasing or decreasing the rotational speed of the printing cylinders in the individual printing units of the printing machine. In other words, the rotational speed of the printing cylinders is changed according to a predefined timing function. Generally, the rotational speed of the printing cylinders is increased according to a speeding-up ramp that is as flat as possible, i.e., in a relatively large time interval. The large time interval avoids the situation in which after a first sheet has run into the machine and the individual printing cylinders have been switched to the printing-on position, the load moment caused by the additional starting torsion leads to a register offset or doubling phenomena on the printed product. Increasing the rotational speed of the printing cylinders as slowly as possible also has the advantage of allowing the inking and/or damping solution feeds to adapt the metering of the ink and/or damping solution to the increasing rotational speed of the printing cylinders.
Particularly in the case of sheet-fed offset printing machines having a speed-controlled direct current motor within the main drive, the rotational speed of the printing cylinders is often slowed down according to a very steep retardation ramp, i.e., in a relatively short time interval. Thus, it is only when the rotational speed of the printing cylinders is rapidly decreased that very high moments act on the printing cylinder or printing units and cause the drive trains to rotate relative to each other because of elasticity. It is precisely in this operating situation that register offsets or doubling phenomena occur. Moreover, when the rotational speed of the printing cylinders is reduced this rapidly, it is not possible to adapt the metering of the ink and/or damping solutions to the decreasing rotational speed of the printing cylinders given the design limitations of the inking and/or damping units.
DE 4 132 766 A1 discloses a speed regulating device for the drive motor of a printing machine that allows direct influencing of the torque acting on the drive train. However, it is not possible to flexibly adapt the speeding-up or slowing-down ramps as a function of the operating state of the machine (e.g., as a function of whether the printing cylinders are in a printing-on or printing-off position). Thus, although this speed regulating device limits the torque when the printing machine is slowed down, the slowing down ramps are not adapted in terms of their duration or slope to the adjusting motors effecting the ink and/or damping solution feed.
DE 4 137 482 A1 discloses a controller arranged between the converter control device and the machine control system for slowing-down the drive motor of a printing machine. The controller includes a rotational speed set-point timer and implements the slowing-down operation with reference to a speed/time coordinate system according to a three-phase characteristic curve. Using this controller, rapid slowing down is limited with phases of soft slowing down at the start and end of a slow down period. As a result, shock-like loading during the beginning and the end of the slowing-down operation is reduced. The disadvantages explained above, with respect to the possibility of tracking the ink and/or damping solution feed via appropriate adjustments while slowing down, are not overcome.
DE 3 214 707 A1 discloses a control system for a printing machine drive motor which has a starting-up torque control system to influence the starting-up torque when restarting the continuous printing speed for a drive motor of a printing machine. With this system, however, only those register offset or doubling phenomena which are caused by torsion when speeding up from a basic speed to a continuous printing speed are avoided or reduced.
EP 0 243 728 B1 discloses a safety system for a printing machine in which the main drive can be stopped under program control in accordance with the operating situations present. However, this stopping under memory and program control is not carried out in order to adapt the slowing down to the printing process.